In view of the current trend of enhancing speed and density in the LSI technique, it is desired today to make the lines more fine, increase the number of layers of electronic circuit wiring and improve the electric characteristics further. For satisfying these requirements, studies are being directed toward manufacturing a multi-layer wiring board by the use of an organic insulating material excellent in flatness, heat resistance, dimensional stability and dielectric characteristics as a substrate.
At the time of forming a layer or a wiring composed of a conductive material and especially of copper on an organic insulating resin substrate by the wet or dry plating process, the most important problem is adhesion between the metallic layer or wiring and the resin substrate board. According to prior art, it has been conventional to roughen the surface of resin board by the method of soft etching or a method of previously incorporating a rubber component into the substrate resin and dissolving out the rubber with a solvent and thereby improve the adhesion of metallic layer deposited on the resin surface by the anchoring effect or mechanical inter locking effect. Details of such prior techniques are summarized in Polymer Surface Modification: Relevance to Adhesion, edited by K. L. Mittal, published by VSP, 1996.
Such prior techniques, however, require to form a concavo-covex pattern having a depth of several tens microns on the substrate surface in order to realize a sufficient adhesion, so that such techniques are not suitable for applications in which a metallic fine pattern having a width smaller than several tens microns has to be formed on the surface. Further, the wiring obtained according to such techniques is unusable for applications for high frequency wave, because the wiring has a concavo-convex pattern reproducing the roughened surface. Further, the process of roughening usually involves a treatment using a sulfuric acid-chromic acid mixture, and the use of such a strong and dangerous corroding solution in a large amount is undesirable form the viewpoint of safety, hygiene and environmental protection. Thus, it is being studied today to replace the anchoring effect or mechanical inter locking effect with an effect of chemical interaction by which the adhesion between resin board and deposited metal can be enhanced.
As the method for realizing a sufficient adhesion between a flat and smooth resin surface and a metal by a chemical interaction, the methods disclosed in Japanese Patent No. 2622016, JP-A-6-256960 and JP-A-11-117060 can be referred to, wherein a surface of a resin containing an amide bond or imide bond in its chemical structure is treated with an aqueous solution containing a mixture of hydrazine hydrate or ethylenediamine and alkali metal hydroxide or treated with a plasma, and then the surface is treated with a catalyst, and then a metallic layer is formed by the electroless plating process. In JP-A-11-220254, there is disclosed a metallic layer-coated resin substrate utilizing the phenomenon that a metal oxide can be bonded, with a high adhesive strength, to a resin surface having an amide bond or an imide bond in its chemical structure and treated with an alkaline aqueous solution, and a method for manufacturing such a resin substrate. If a resin surface is treated with an alkaline aqueous solution or by means of a plasma, a quality-changed resin layer is formed on the resin surface. However, if the quality-changed resin layer exists at the interface between a plating metal layer and a resin, there can often appear an important defect in the reliability of the metallic layer-coated resin substrate. For example, if the substrate is subjected to a pressure-cooker test (PCT test) which comprises heating a board under a high humidity condition, the adhesion between plating metal layer and resin becomes bad extremely, and a swelling or peeling of the metallic layer sometimes occurs, and the product thus obtained is by no means usable. Further, the extent of the quality change and the thickness of the quality-changed resin layer are markedly influenced by intensity, time and temperature of the treatment using the aqueous alkali solution or plasma, and by the formulation of the resin, so that it is difficult to control the extent of quality change and thickness so as to come to optimum values, in high reproducibility. If the quality-changed layer is not formed under optimum conditions, the quality-changed resin layer exhibits no sufficient adhesion to the metallic layer deposited thereon and, in some cases, the catalyst necessary for the electroless plating process cannot be given thereto satisfactorily.
Further, in JP-A-2-131934, it is mentioned that the adhesive force between copper foil and a heterocyclic ring-containing resin (for example, polyimide resin, polyamide-imide resin, etc.) coated onto the copper foil can be improved by providing a layer of copper oxide on the surface of the copper foil. Usually, if a resin is coated onto copper foil in the presence of atmospheric air, a copper oxide layer is formed between the resin and the copper foil. If a heterocyclic ring-containing resin such as polyimide resin, polyamide-imide resin or the like is coated on a flat copper foil, however, the adhesive force between the resin and the foil is not sufficient, so far as evaluated substrated on the force required for peeling off the resin from the foil. Thus, in the actual manufacture of flexible board, etc., a necessary adhesive force is achieved by roughening the surface of copper foil.
JP-A-10-183358 discloses a method for forming a metallic layer on a flat resin surface with a good adhesion without treatment with alkaline aqueous solution or plasma, which comprising carrying out an electroless plating on a resin composition having a combination of a chemical structure containing a nitrogen-hydrogen bond and a salt-forming functional group such as carboxyl group, sulfonic acid group, phosphoric acid group or the like. However, a blending use of a salt-forming agent such as a compound having an ionically dissociating group into a resin composition brings about deterioration of dielectric characteristics, and a metallic layer-coated resin board using such a blended mixture is not usable in electronic materials such as wiring board and the like.
It is an object of this invention to provide a member exhibiting an enhanced adhesion to metal deposited on a resin surface without roughening the surface of the substrate resin, and to a method for manufacturing said member. Preferably, the object of this invention is to obtain a sufficient adhesion without carrying out a quality-changing treatment of resin surface using an alkaline aqueous solution or plasma, nor carrying out a blending of a compound having ionically dissociating group into the resin, said treatment and said blending both deteriorating the reliability of metallic layer-containing member or its electric properties and obstructing a stable manufacture of the metallic layer-containing member, and to provide a build-up type multi-layer wiring board, a flexible wiring board, a wiring substrate board for multi-chip module and a member for forming a plating metal layer which use the above-mentioned member and have an excellent reliability.